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View Full Version : Engine RPM falls switching into neutral

shoottothrill
03-02-2021, 09:57 PM
Hey guys, I've got a KA S14, stock ECU, stock engine, stock most things. It is a factory auto, manual swapped, still using the stock 3D auto ecu.

What I'm finding is that when I have the clutch in 1st gear, it'll idle where I would expect, 800-900 rpm. Without moving anything else (clutch still in), and switching into neutral, the idle will fall to 500-600 rpm.

If the idle fell the opposite way, neutral to 1st, that would make a fair bit more sense to me. Is this a byproduct of having the auto ecu still in? Would swapping in a 3c manual ecu fix the issue? Anybody ever run into this issue?

Thanks for the info!
Silv1401
03-04-2021, 08:44 PM
Does it cause drivability issues?

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shoottothrill
03-04-2021, 08:46 PM
Does it cause drivability issues?

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No, it's just very annoying.
Silv1401
03-04-2021, 10:42 PM
Duh fuq you posting for then? It's a 240. If you don't have the wherwithal to figure out the bug, then just gonna have to live with it lol. Also, fwiw, I don't think I've ever seen an actual good piece of advice come from this forum for anyone running an automatic transmission, besides the proverbial "manual swap it"

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shoottothrill
03-04-2021, 10:44 PM
...if you'd actually read far enough, it is manual swapped. I'm just looking if anyone else has run into it.

If you haven't, you can see yourself out my dude
Silv1401
03-05-2021, 01:58 AM
Pfft, my bad, re read it.

Weird issue, could be the cpu getting signal from the neutral position sensor (if you happened to wire that in for some reason,) and dropping revs to normal idle speed. Likewise if you wired the top position sensor in as well, then the CPU would be getting signal for being in gear, so it is raising the idle in anticipation of counteracting the engine load. Theoretically. You could get under there and just unplug everything but the reverse light and speed sensor, and see if it changes anything. Those are the only two you really need anyways.

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